Several companies have developed technology for the manufacture of PDO starting with ethylene oxide as the main raw material. The ethylene oxide is reacted with synthesis gas (syngas), a mixture of carbon monoxide and hydrogen, which may be obtained by steam reforming of natural gas or partial oxidation of hydrocarbons. The idealized reaction of ethylene oxide (EO) with syngas to yield PDO is shown below:EO+CO+2H2→PDO
U.S. Pat. Nos. 4,873,378, 4,873,379, and 5,053,562 from Hoechst Celanese describe a single step reaction using 2:1 (molar) syngas at 110 to 120° C. and about 1000 psig (6900 kPa) to give 65 to 78 mole percent yield of PDO and precursors thereof. The catalyst system used consisted of rhodium, various phosphines, and various acids and water as promoters.
U.S. Pat. Nos. 5,030,766 and 5,210,318 to Union Carbide describe the reaction of EO with syngas in the presence of rhodium-containing catalysts. At 110° C. and 1000 psig (6900 kPa) of 2:1 molar syngas, a selectivity of up to 47 mole percent was achieved but the combined rate of formation of PDO and 3-hydroxy propanal was quite low at 0.05 to 0.07 moles per liter per hour. Better results were achieved by increasing the ratio of phosphoric acid promoter to rhodium catalyst.
U.S. Pat. Nos. 5,256,827, 5,304,686, and 5,304,691 to Shell Oil described PDO production from EO and syngas utilizing tertiary phosphine-complexed cobalt carbonyl catalysts. Reaction conditions of 90 to 105° C. and 1400 to 1500 psig (9650 to 10,340 kPa) of syngas (1:1 molar ratio) for three hours produced selectivities in the range of 85 to 90 mole percent and the EO conversion was in the range of 21 to 34 percent. Later work reported increased selectivity and EO conversion.
U.S. Pat. No. 5,527,973 describes a method for the purification of PDO which contains carbonyl byproducts including acetals. An aqueous solution of a carbonyl-containing PDO is formed having a pH less than 7 and then a sufficient amount of base is added to this solution to raise the pH to above 7. The solution is then heated to distill most of the water from it and then the remaining basic solution is heated to distill most of the PDO from the basic solution providing a PDO composition having a lower carbonyl content than the starting composition. This process has several steps and it would be a commercial advantage to provide a method which would lower the carbonyl content in fewer process steps.